Fission Products in National Atmospheric Deposition 

Program—Wet Deposition Samples Prior to and Following 

the Fukushima Dai-Ichi Nuclear Power Plant Incident, 

March 8–April 5, 2011

Open-File Report 2011–1277

U.S. Department of the Interior

U.S. Geological Survey
Fission Products in National Atmospheric Deposition 

Program—Wet Deposition Samples Prior to and Following 

the Fukushima Dai-Ichi Nuclear Power Plant Incident, 

March 8–April 5, 2011

By Gregory A. Wetherbee, Timothy M. Debey, Mark A. Nilles, Christopher M.B. Lehmann, and David A. Gay

Open-File Report 2011–1277

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012 

For product and ordering information:

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its natural and living resources, natural hazards, and the environment:

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Suggested citation:

Wetherbee, G.A., Debey, T.M., Nilles, M.A., Lehmann, C.M.B., and Gay, D.A., 2012, Fission products in National 

Atmospheric Deposition Program—Wet deposition samples prior to and following the Fukushima Dai-Ichi Nuclear 

Power Plant incident, March 8–April 5, 2011: U.S. Geological Survey Open-File Report 2011–1277, 27 p. 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
iv

Contents

Abstract ......................................................................................................................................................................... 1

Introduction.................................................................................................................................................................... 1

National Atmospheric Deposition Program Sites........................................................................................................ 2

Purpose and Scope.................................................................................................................................................... 5

Methods......................................................................................................................................................................... 5

Adaptation of National Atmospheric Deposition Program Networks........................................................................... 5

Analysis of Filtered Particulates ................................................................................................................................. 6

Analysis of Whole-Water Wet Deposition Samples.................................................................................................... 6

Sample Analysis by Gamma Spectrometry.............................................................................................................. 13

Quality Assurance.................................................................................................................................................... 15

Fission Products .......................................................................................................................................................... 16

Summary and Conclusions.......................................................................................................................................... 26

Acknowledgments........................................................................................................................................................ 26

References Cited......................................................................................................................................................... 27

Figures

1. Active (2011) and formerly active National Atmospheric Deposition Program/National Trends Network

(NTN) sites .......................................................................................................................................................... 3

2. Active (2011) and formerly active National Atmospheric Deposition Program Mercury Deposition 

Network (MDN) sites ........................................................................................................................................... 4

3. Flow diagram of sample processing for analysis of radionuclides in National Atmospheric Deposition 

Program / National Trends Network and Mercury Deposition Network samples ................................................. 7

4. Gamma ray spectra for wet-deposition sample from National Atmospheric Deposition Program site 

SD04 (March 22–29) with manually quantified cesium-134 peak...................................................................... 15

5. Spatial distribution of iodine-131 (I-131) activities in National Atmospheric Deposition Program (NADP) 

samples from the 48 contiguous United States during March 15–29, 2011 ...................................................... 19

6. Spatial distribution of iodine-131 (I-131) deposition calculated from measured activities and rain-gage

depths from National Atmospheric Deposition Program (NADP) sites in the 48 contiguous United States

during March 15–April 5, 2011 .......................................................................................................................... 20

7. Spatial distribution of estimated cesium-134 (Cs-134) activities in National Atmospheric Deposition 

Program (NADP) samples from the 48 contiguous United States during March 15–29, 2011 .......................... 21

8. Spatial distribution of cesium-134 (Cs-134) deposition calculated from estimated activities and measured 

rain-gage depths from National Atmospheric Deposition Program (NADP) sites in the 48 contiguous 

United States during March 15–April 5, 2011.................................................................................................... 22

9. Spatial distribution of detected cesium-137 (Cs-137) activities in National Atmospheric Deposition 

Program (NADP) samples from the 48 contiguous United States during March 15–29, 2011 .......................... 23

10. Spatial distribution of cesium-137 (Cs-137) deposition calculated from measured activities and 

rain-gage depths from National Atmospheric Deposition Program (NADP) sites in the 48 contiguous

United States during March 15–April 5, 2011.................................................................................................... 24

11. Spatial distribution of cesium-134 (Cs-134) and cesium-137 (Cs-137) measured activities and 

calculated deposition values from National Atmospheric Deposition Program (NADP) sites in Alaska 

during March 15–April 5, 2011. (pCi/L, picoCuries per liter; Bq/m2, Becquerels per square meter) .................. 25
v

Tables

1. NADP weekly wet-deposition samples, March 8, 2011–April 5, 2011 for gamma spectrometry analysis............ 8

2. Fission product isotope activities, associated precipitation depths, and calculated deposition values for 

National Atmospheric Deposition Program wet-deposition samples collected during March 15–April 5, 2011.. 17

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

meter (m) 1.094 yard (yd)

Area

square meter (m2) 0.0002471 acre

Volume

liter (L) 1.057 quart (qt)

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)

Energy

1,000 electron volts (keV) 1.602 x 10-16 joules

1,000,000 electron volts (MeV) 1.602 x 10-13 joules

Activity

microCurie (μCi) 1 x 106 Curies

Becquerels per liter (Bq/L) 27.03 picoCuries per liter (pCi/L)

Deposition (flux to Earth’s surface)

Becquerels per square meter (Bq/m2) 27.03 picoCuries per square meter (pCi/m2)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Activities of isotopes in water are given either in picoCuries per liter (pCi/L) or Becquerels per liter (Bq/L).

Deposition (flux) of isotopes to Earth’s surface is given in Becquerels per square meter (Bq/m2).
vi

Abbreviations and Acronyms

Abbreviation Full name

ACM AeroChem Inc. Metrics Model 301 precipitation collector

BrCl bromine monochloride

Bq/m2 Becquerels per square meter

BQS Branch of Quality Systems

CAL Central Analytical Laboratory

Cs-134 cesium-134 isotope

Cs-137 cesium-137 isotope

Eu-152 europium-152 isotope

GIS Geographic Information System

HAL Mercury Analytical Laboratory

HCl hydrochloric acid

HPGe high-purity germanium 

I-131 iodine-131 isotope

keV thousand electron volts

MDN Mercury Deposition Network

NADP National Atmospheric Deposition Program

NIST National Institute of Standards and Technology

NTN National Trends Network

pCi/L picoCuries per liter

pCi/m2 picoCuries per square meter

QA quality assurance

SAP sampling and analysis plan

USGS United States Geological Survey
1

Fission Products in National Atmospheric Deposition 

Program—Wet Deposition Samples Prior to and Following 

the Fukushima Dai-Ichi Nuclear Power Plant Incident, 

March 8–April 5, 2011 

By Gregory A. Wetherbee,1 Timothy M. Debey,

1 Mark A. Nilles,1 Christopher M.B. Lehmann,2 and David A. Gay3

Abstract

Radioactive isotopes I-131, Cs-134, or Cs-137, products of uranium fission, were measured at 

approximately 20 percent of 167 sampled National Atmospheric Deposition Program monitoring sites in 

North America (primarily in the contiguous United States and Alaska) after the Fukushima Dai-Ichi 

Nuclear Power Plant incident on March 12, 2011. Samples from the National Atmospheric Deposition 

Program were analyzed for the period of March 8–April 5, 2011. Calculated 1- or 2-week radionuclide 

deposition fluxes at 35 sites from Alaska to Vermont ranged from 0.47 to 5,100 Becquerels per square 

meter during the sampling period of March 15–April 5, 2011. No fission-product isotopes were 

measured in National Atmospheric Deposition Program samples obtained during March 8–15, 2011, 

prior to the arrival of contaminated air in North America.

Introduction

On March 11, 2011, a magnitude 9.0 earthquake centered off the Pacific Coast of Japan 

triggered a tsunami and a 14-meter (m)-high tidal wave that inundated the Fukushima Dai-Ichi Nuclear 

Power Plant near Sendai, Japan (Wakeford, 2011). The facility was left without electric power, which 

resulted in failure of the cooling systems for its six nuclear reactors (Wakeford, 2011). The resultant loss 

of containment due to steam explosions and the breach of fuel elements in reactors and cooling ponds

lead to the discharge of radioactive materials into the atmosphere, including fission-product isotopes

iodine-131 (I-131, half-life 8.0 days), cesium-134, and -137 (Cs-134 half-life 2.1 years; Cs-137 half-life 

30.2 years) (Lide, 1990). These isotopes were reported in many different countries in the Northern 

Hemisphere at variable but low levels (Wakeford, 2011). 

In response to the incident, the United States Geological Survey (USGS), lead agency within the 

National Atmospheric Deposition Program4 (NADP), collaborated with NADP personnel to quickly 

develop sampling and analysis plans and quality assurance protocols to monitor the radioactive fallout 

 1 U.S. Geological Survey, Denver, Colo.

2 University of Illinois, Prairie Research Institute, Illinois State Water Survey, Central Analytical Laboratory, Champaign, Ill. 3 University of Illinois, Prairie Research Institute, Illinois State Water Survey, National Atmospheric Deposition Program 

Office, Champaign, Ill.

4 The NADP is a focused and coordinated effort of many different organizations, including federal, state, tribal, and local 

governmental agencies, educational institutions, private companies, and non-governmental agencies, to monitor atmospheric 

deposition throughout North America (http://nadp.sws.uiuc.edu/).
2

over North America. NADP sample management and handling protocols were adapted to archive both 

filter samples and excess whole-water wet-deposition samples during the period of March 8–April 5, 

2011. USGS measured 456 samples by gamma spectrometry for radioactive isotopes for both filterable 

solids from the precipitation (280 samples) and whole-water wet-deposition (176 samples).

National Atmospheric Deposition Program Sites

Sites owned by the NADP in both the NADP’s National Trends Network (NTN) and Mercury 

Deposition Network (MDN) were used to monitor fission-product isotope fallout. The NTN is described 

by Nilles (2001), and the MDN is described by Prestbo and Gay (2009). Standard operating procedures 

for NTN are available at http://nadp.sws.uiuc.edu/lib/manuals/opman.pdf, and for MDN at 

http://nadp.sws.uiuc.edu/lib/manuals/mdnopman.pdf, both accessed October, 2011.

As of summer 2011, precipitation was being collected weekly from 251 sites in the NTN and 

105 sites in the MDN within Canada and the United States, including Alaska, Puerto Rico, and the U.S.

Virgin Islands (figs. 1 and 2). Both NTN and MDN sites are equipped with automatic precipitation 

collectors that open to the atmosphere at the onset of precipitation and close at cessation of precipitation 

to collect wet-only atmospheric deposition. While the precipitation collectors obtain representative 

samples for chemical analysis, they do not provide precipitation depth measurements of consistent 

accuracy. Therefore, each site is equipped with a rain gage to measure precipitation depth for 

calculation of the mass of selected constituents per unit area (flux) to the landscape. Radioactive isotope 

deposition was calculated by equation 1.

Deposition, in picoCuries per square meter (pCi/m2

) A Ppt pCi L× mm = / , (1)

where: ApCi/L is activity of radioactive isotope, in picoCuries per liter (pCi/L), and

Pptmm is precipitation depth, in millimeters (mm) as measured by the rain gage

applied over a 1-square-meter area.

Comparison of NADP measurements to data obtained from other monitoring entities requires 

conversion of deposition in picoCuries per square meter to Becquerels per square meter (Bq/m2).

Because 3.7 × 1010 Bq equals 1 × 1012 pCi, the units are converted as follows in equation 2.

Deposition, in picocuries per square meter × 0.037 = Deposition, in Becquerels per square meter (2)
3

Figure 1. Active (2011) and formerly active National Atmospheric Deposition Program/National Trends Network (NTN) sites.
4

Figure 2. Active (2011) and formerly active National Atmospheric Deposition Program Mercury Deposition Network (MDN) sites.
5

Weekly composite NTN and MDN whole-water precipitation samples are removed from the 

automated collectors every Tuesday morning at approximately 9:00 a.m. local time. In this report, 

NADP site identifiers are used for brevity. The identifiers consist of the state or country abbreviation 

and a one- or two-digit number. For example, site CO90 is in Colorado (CO) and CAN5 is in Quebec, 

Canada.

Purpose and Scope

The purpose of this report is to present the methods and results from sampling and analysis of 

the radioactive isotopes iodine-131 (I-131), cesium-134 (Cs-134), and cesium-137 (Cs-137) in NADP 

wet-deposition samples during the period of March 8–April 5, 2011. These isotopes are collectively 

referred to as “fission products” hereinafter. This report describes sample collection, processing, and 

analysis methods for unfiltered wet-deposition samples and filtered particulates (filter samples). The 

report also presents quality assurance (QA) protocols and results.

Gamma-ray spectra for naturally occurring gamma-emitting isotopes were obtained as part of 

this study, but these spectral components were not quantified for this report. Health risk assessments and 

comparison of measured activities to water-quality or health-related standards are beyond the scope of 

this report. This report provides no interpretation with respect to atmospheric transport processes.

Deposition of fission products is estimated using the measured activities and precipitation-depth 

measurements obtained from the rain gages at each NADP site. Selected sites in the southern and 

southeastern regions of the Nation were excluded from this study because samples from these sites were 

used for a plant pathogen study, for which the entire sample volume is filtered and needed for analysis

in that study. An example of a similar NADP plant pathogen study is described by Barnes and others 

(2009).

Methods

Adaptation of National Atmospheric Deposition Program Networks

On March 14, 2011, within 48 hours (hr) after the release of radioactive material into the 

atmosphere at the Fukushima Dai-Ichi Nuclear Power Plant in Japan on March 12, 2011, the NADP 

coordinated with the USGS to put a plan in place to measure radionuclide fallout in NADP wetdeposition samples. NADP/NTN began saving excess unfiltered wet-deposition samples with special 

handling and analysis protocols, beginning with the sample-collection week of March 8–15, 2011, prior 

to any documented measurement of radioactive fallout in North America (Leon and others, 2011).

Sampling and analysis plans (SAPs) were developed and reviewed by USGS and NADP personnel. 

These plans defined methodology for sample archive, preservation, analysis, and quality assurance for 

both the filter samples and wet-deposition samples. The SAPs delineated North America into three 

regions: western, central, and eastern. Samples were prioritized for analysis by region with the western 

region given first priority, and the eastern region given last priority. The goal of the prioritization 

scheme was to analyze samples with the greatest likelihood of containing fission products first, with a 

particular focus on short-lived radionuclides such as I-131. It was assumed that radionuclide 

concentrations in wet-deposition samples would be proportional to the west-to-east (prevailing wind 

direction; Takemura and others, 2011) distance from Japan.

The NTN samples are collected in clean, 29.4-centimeter (cm) diameter, 13.2-liter (L), 

polyethylene buckets. The MDN samples are collected using a borosilicate glass sampling train 

consisting of a 120.1- mm diameter funnel and thistle tube that directs the precipitation to a 2-L 

borosilicate bottle pre-charged with 20 milliliters (mL) of 1-percent (volume : volume) hydrochloric 
6

acid (HCl) for mercury preservation. Aerochem Metrics, Inc. Model 301(ACM) precipitation collectors

(modified for MDN) have an auxiliary collection chimney that may be fitted with polyethylene funnels 

and bottles for collection of additional samples that are not preserved. Excess samples from both 

networks were obtained for gamma spectrometry analysis of radioactive isotopes. 

Archive of MDN excess samples in Washington and Alaska was implemented on March 18, 

2011. MDN samples were treated with 1 percent (volume : volume) bromine monochloride (BrCl) for 

mercury analysis, and the unused portion was split into clean borosilicate glass bottles for gamma 

spectrometry analysis of radioactive isotopes. In addition, polyethylene bottles were shipped to MDN 

site AK00 at Dutch Harbor, Alaska, and 18WA in Seattle, Wash. These bottles were installed in the 

auxiliary sample collection chimneys of the precipitation collectors. Samples collected in the 

polyethylene bottles were not preserved, and they were shipped first to the Mercury Analytical 

Laboratory (HAL) at Frontier Global Sciences, Inc. in Seattle, Wash. and then to Denver, Colo. for 

gamma spectrometry analysis.

Analysis of Filtered Particulates

Samples from NTN are decanted from the collector buckets to 1-L Nalgene bottles in the field 

and shipped without preservation to the NADP Central Analytical Laboratory (CAL) located in 

Champaign, Ill. CAL filters approximately 250 mL of NTN samples through 47-mm diameter, 0.45-

micron (μm) pore-size, polysulfone filters. CAL saved the filters from NTN samples for the weeks 

ending March 15, March 22, and March 29, 2011 in labeled plastic petri dishes and shipped them to

Denver, Colo., for gamma spectrometry analysis. Radioactive isotopes released at the Fukushima DaiIchi Nuclear Power Plant were assumed to have affinity for adsorption onto aerosol particles, which are 

washed out of the atmosphere in wet deposition. Therefore, the NTN filters were initially targeted for 

gamma spectrometry analysis. As shown later herein, this assumption proved to be invalid.

Analysis of Whole-Water Wet Deposition Samples

After analysis of the filter samples was completed, the archived, unfiltered NTN wet-deposition 

samples for the weeks ending March 22 and March 29, 2011 were shipped to the USGS Branch of 

Quality Systems (BQS), located in the USGS National Water Quality Laboratory in Denver, Colo. BQS

added Ultrex nitric acid, obtained from J.T. Baker, Center Valley, Penn., to each 1-L Nalgene container 

according to sample volume (estimated by sample weight) such that each sample contained 

approximately 0.5 percent nitric acid by volume. The samples were shaken and then placed in a warmwater bath for 1 hr to desorb radioactive isotopes from the bottle walls. The acidified samples were 

removed from the bath and allowed to leach for 24 hr prior to compositing of samples by site.

Precipitation-depth-weighted, 2-week composite samples were made for each site by measuring 

aliquots from the acidified weekly samples in proportion to the measured precipitation depths for each 

week. For example, if 6 mm and 4 mm of precipitation were measured for the weeks ending March 22 

and March 29, respectively, then 60 percent of the 2-week composite volume was obtained from the 

March 22 sample and 40 percent was obtained from the March 29 sample. For some sites, no 

precipitation was measured during one of the weeks, in which case the 2-week composite was obtained 

exclusively by the sample for the week with precipitation. There were also instances where precipitation 

was sampled for both weeks, but insufficient volume was available for archive. In these cases, the entire

sample volumes were analyzed, and it was noted that no compositing was possible. Figure 3 illustrates 

how NADP samples were processed for analysis of radionuclides. Table 1 provides information for the 

representation and composition of each sample. For convenience, table 1 also lists any fission-product 

isotopes detected at each site.
7

Figure 3. Flow diagram of sample processing for analysis of radionuclides in National Atmospheric Deposition 

Program / National Trends Network and Mercury Deposition Network samples.
8

Table 1. NADP weekly wet-deposition samples, March 8, 2011–April 5, 2011, for gamma spectrometry analysis.

[NADP, National Atmospheric Deposition Program; NTN, National Trends Network; MDN, Mercury Deposition Network; 

Trace, auxiliary trace metal sample; mm, millimeters; mL, milliliters; Cs-134, cesium-134; Cs-137, cesium-137; I-131, 

iodine-131]

NADP site Network

Represented sampling 

period

Total 

precipitation 

(mm)

Radioactive isotopes 

detected

Analyzed 

sample volume 

(mL)

Samples for NTN sites with 1 dry week and standard weekly MDN samples

18WA MDN / Trace 3/15–3/22/11 15.5 - 789

18WA MDN / Trace 3/22–3/29/11 13.7 - 10

18WA MDN / Trace 3/29–4/05/11 34.3 - 66

AK00 MDN 3/16–3/23/11 86.0 Cs-134, Cs-137 302

AK00 MDN 3/23–3/29/11 14.5 - 21

AK02 NTN 3/15–3/22/11 11.2 Cs-137 303

AK05 MDN 3/08–3/17/11 22.4 - 221

AK05 MDN 3/29–4/05/11 32.8 - 271

AK98 MDN 3/22–3/29/11 16.5 Cs-137 57.4

AK98 MDN 3/29–4/06/11 113 - 1,167

AL03 NTN 3/22–3/29/11 11.7 - 457

CA20 MDN 3/22–3/29/11 126 - 1,325

CA20 MDN 3/29–4/05/11 15.2 - 59

CA88 NTN 3/22–3/29/11 58.6 - 634

CAN5 NTN 3/15–3/22/11 12.7 - 520

CO98 NTN 3/22–3/29/11 54.9 Cs-134, Cs-137 222

CT15 NTN 3/15–3/22/11 22.1 - 622

IL11 NTN 3/15–3/22/11 9.1 - 317

IL46 NTN 3/22–3/29/11 4.8 - 128

IL63 NTN 3/22–3/29/11 20.6 Cs-134, Cs-137 500

IL78 NTN 3/22–3/29/11 13.0 Cs-134, Cs-137 549

KY10 NTN 3/22–3/29/11 7.4 - 276

KY99 NTN 3/22–3/29/11 10.7 - 473

MA08 NTN 3/15–3/23/11 26.2 - 629

ME00 NTN 3/15–3/22/11 12.4 - 40
9

Table 1.—Continued 

NADP site Network

Represented sampling 

period

Total 

precipitation 

(mm)

Radioactive isotopes 

detected

Analyzed 

sample volume 

(mL)

Samples for NTN sites with 1 dry week and standard weekly MDN samples

ME02 NTN 3/15–3/22/11 16.0 - 408

ME04 NTN 3/15–3/23/11 10.1 - 289

ME08 NTN 3/15–3/22/11 10.7 - 256

ME96 NTN 3/15–3/22/11 23.4 - 638

MI48 NTN 3/15–3/22/11 22.9 - 613

MI51 NTN 3/15–3/22/11 13.9 - 562

MI98 NTN 3/15–3/22/11 23.1 - 300

MN08 NTN 3/15–3/22/11 17.3 - 625

MN18 NTN 3/15–3/22/11 7.9 - 89

MN99 NTN 3/15–3/22/11 16.3 - 426

MO03 NTN 3/22–3/29/11 10.7 Cs-134, Cs-137 401

MO05 NTN 3/22–3/29/11 26.4 Cs-134, Cs-137 649

MT00 NTN 3/22–3/29/11 7.1 - 148

NC34 NTN 3/22–3/29/11 17.8 - 673

NE15 NTN 3/22–3/29/11 13.7 - 602

NH02 NTN 3/15–3/22/11 27.9 - 666

NJ00 NTN 3/15–3/22/11 28.7 - 694

NY20 NTN 3/15–3/22/11 22.6 - 583

NY22 NTN 3/15–3/22/11 17.2 - 679

NY29 NTN 3/15–3/22/11 16.5 - 539

PA72 NTN 3/17–3/25/11 34.3 - 657

SC05 NTN 3/22–3/29/11 44.5 - 553

SD04 NTN 3/22–3/29/11 21.6 Cs-134, Cs-137 682

SD99 NTN 3/21–3/29/11 14.4 Cs-137 362

TN04 NTN 3/22–3/29/11 48.5 - 610

TN11 NTN 3/21–3/29/11 40.6 - 724

TN14 NTN 3/22–3/29/11 20.0 Cs-134, Cs-137 577

VI01 NTN 3/15–3/22/11 5.1 - 36

VT01 NTN 3/15–3/22/11 18.0 Cs-134, Cs-137 694

WA03 MDN 3/08–3/15/11 226. - 1,197

WA03 MDN 3/15–3/22/11 39.4 - 315

WA03 MDN 3/22–3/29/11 45.7 - 293

WA03 MDN 3/29–4/05/11 159. Cs-134, Cs-137 989

WI99 NTN 3/15–3/23/11 50.8 - 723
10

Table 1.—Continued 

NADP site Network

Represented sampling 

period

Total 

precipitation 

(mm)

Radioactive isotopes 

detected

Analyzed 

sample volume 

(mL)

Samples for NTN sites with 2 wet weeks, but insufficient volume for 2-week composite.

01MA NTN 3/15–3/22/11 20.1 - 448

AZ03 NTN 3/15–3/22/11 18.8 - 170

CA42 MDN 3/22–3/29/11 170. Cs-134, Cs-137 164

CA67 NTN 3/15–3/22/11 9.7 - 261

CO02 NTN 3/22–3/29/11 109. Cs-134, Cs-137 290

CO08 NTN 3/15–3/22/11 50.5 - 574

CO10 NTN 3/22–3/29/11 21.8 Cs-134, Cs-137 900

CO19 NTN 3/15–3/22/11 17.5 - 494

CO94 NTN 3/22–3/29/11 8.6 Cs-137 95

CO97 NTN 3/15–3/22/11 23.1 - 342

ID11 NTN 3/24–3/31/11 9.7 - 448

IN22 NTN 3/15–3/22/11 9.1 - 247

KY19 NTN 3/15–3/22/11 12.4 - 538

MA01 NTN 3/15–3/22/11 19.1 - 666

MN23 NTN 3/22–3/29/11 34.3 Cs-137 640

MT98 NTN 3/22–3/29/11 5.3 - 139

NC03 NTN 3/22–3/29/11 27.4 - 711

NC29 NTN 3/22–3/29/11 17.5 - 554

NC35 NTN 3/22–3/29/11 13.5 - 454

NC41 NTN 3/22–3/29/11 16.0 - 355

NJ99 NTN 3/22–3/29/11 16.8 - 522

NV03 NTN 3/15–3/23/11 18.3 - 533

NY98 NTN 3/15–3/22/11 14.0 - 467

OH09 NTN 3/15–3/22/11 12.7 - 458

OH49 NTN 3/15–3/22/11 15.2 - 414

OR18 NTN 3/15–3/22/11 21.8 - 641

SC06 NTN 3/22–3/29/11 60.5 - 678

TN00 NTN 3/22–3/29/11 26.9 - 673

UT01 NTN 3/16–3/22/11 20.8 - 378

UT99 NTN 3/22–3/29/11 14.5 - 204

VA99 NTN 3/22–3/29/11 8.6 Cs-137 111

VT99 NTN 3/15–3/22/11 11.2 - 220

WI09 NTN 3/15–3/22/11 9.7 - 360

WI25 NTN 3/15–3/22/11 8.1 - 221

WI28 NTN 3/15–3/22/11 17.0 - 94

WV05 NTN 3/15–3/22/11 44.7 - 636

WY00 NTN 3/22–3/29/11 106. - 244
11

Table 1.—Continued 

NADP site Network

Represented sampling 

period

Total 

precipitation 

(mm)

Radioactive isotopes 

detected

Analyzed 

sample volume 

(mL)

Samples for NTN sites with 2 wet weeks, but insufficient volume for 2-week composite.

WY08 NTN 3/15–3/22/11 32.8 - 652

WY99 NTN 3/22–3/29/11 9.4 Cs-134, Cs-137 239

NTN precipitation-depth-weighted 2-week composite samples.

50CA NTN 3/15–3/29/11 246. - 1,000

CA28 NTN 3/15–3/29/11 246. - 775

CA45 NTN 3/15–3/29/11 212. - 1,000

CA50 NTN 3/15–3/29/11 189. - 1,000

CA66 NTN 3/15–3/29/11 107. Cs-134, Cs-137, I-131 1,000

CA75 NTN 3/15–3/29/11 128. - 1,000

CA76 NTN 3/15–3/29/11 42.9 - 485

CA94 NTN 3/16–3/29/11 60.2 Cs-134, Cs-137 870

CA96 NTN 3/15–3/29/11 231. - 821

CA99 NTN 3/15–3/29/11 235. Cs-134, Cs-137, I-131 1,000

CO15 NTN 3/15–3/29/11 29.2 - 481

CO89 NTN 3/15–3/29/11 92.7 Cs-134, Cs-137 303

CO90 NTN 3/15–3/29/11 48.5 Cs-134, Cs-137, I-131 1,000

CO91 NTN 3/15–3/29/11 34.6 - 717

IA08 NTN 3/15–3/29/11 58.9 - 1,000

IA23 NTN 3/15–3/29/11 18.3 - 548

ID02 NTN 3/14–3/29/11 50.1 - 947

ID03 NTN 3/15–3/29/11 20.8 - 687

IL18 NTN 3/15–3/29/11 20.8 - 589

IN20 NTN 3/15–3/29/11 40.6 - 575

KY03 NTN 3/15–3/29/11 12.4 - 210

KY22 NTN 3/15–3/29/11 27.4 - 735

KY35 NTN 3/15–3/29/11 20.1 - 258

MD07 NTN 3/15–3/29/11 36.6 Cs-137 794

MD08 NTN 3/15–3/29/11 38.1 - 715

MD13 NTN 3/15–3/29/11 40.9 - 786

MD15 NTN 3/15–3/29/11 28.5 - 1,000

MD18 NTN 3/15–3/29/11 32.5 - 1,000

MD99 NTN 3/15–3/29/11 31.0 - 660

ME98 NTN 3/15–3/29/11 43.4 - 771

MI26 NTN 3/15–3/29/11 45.2 Cs-137 930

MI52 NTN 3/15–3/29/11 49.2 - 891

MI53 NTN 3/15–3/29/11 34.5 - 733

MN01 NTN 3/15–3/29/11 45.5 Cs-134, Cs-137 1,000

MN27 NTN 3/15–3/29/11 32.8 - 853
12

Table 1.—Continued 

NADP site Network

Represented sampling 

period

Total 

precipitation 

(mm)

Radioactive isotopes 

detected

Analyzed 

sample volume 

(mL)

NTN precipitation-depth-weighted 2-week composite samples.

MN28 NTN 3/15–3/29/11 27.2 - 167

MT07 NTN 3/15–3/29/11 14.7 Cs-137 308

MT97 NTN 3/15–3/29/11 48.7 - 751

NC06 NTN 3/15–3/29/11 18.1 - 236

NC25 NTN 3/15–3/29/11 103. - 620

NC45* NTN 3/08–3/29/11 88.2 - 1,000

NY01 NTN 3/15–3/29/11 48.5 Cs-134, Cs-137 1,000

NY08 NTN 3/15–3/29/11 24.6 - 552

NY10 NTN 3/15–3/29/11 47.0 Cs-134, Cs-137 1,000

NY68 NTN 3/15–3/29/11 33.5 - 740

NY96 NTN 3/15–3/29/11 17.5 - 252

NY99 NTN 3/15–3/29/11 38.8 - 297

OH17 NTN 3/15–3/29/11 20.9 - 855

OH54 NTN 3/15–3/29/11 14.0 - 606

OH71 NTN 3/15–3/29/31 16.3 - 527

OR10 NTN 3/15–3/29/11 173. Cs-137 1,002

OR97 NTN 3/15–3/29/11 68.6 - 753

PA00 NTN 3/15–3/29/11 26.7 - 340

PA15 NTN 3/15–3/29/11 48.8 - 801

PA18 NTN 3/15–3/29/11 52.6 - 1,000

PA29 NTN 3/15–3/29/11 50.0 - 1,000

PA42 NTN 3/15–3/29/11 49.1 - 1,000

PA47 NTN 3/15–3/29/11 30.0 - 1,000

PR20 NTN 3/15–3/29/11 60.5 - 583

VA00 NTN 3/15–3/29/11 26.4 - 1,000

VA13 NTN 3/15–3/29/11 31.7 - 1,000

VA24 NTN 3/15–3/29/11 28.7 - 529

VA28 NTN 3/15–3/29/11 31.3 - 982

VA98 NTN 3/15–3/29/11 30.2 - 102

WA14 NTN 3/15–3/29/11 97.5 - 1,000

WA19 NTN 3/15–3/29/11 78.0 - 639

WA21 NTN 3/15–3/29/11 45.4 - 838

WA24 NTN 3/15–3/29/11 38.8 - 901

WA98 NTN 3/15–3/29/11 126. Cs-134, I-131 1,000

WA99 NTN 3/16–3/29/11 54.6 Cs-134, I-131 1,000

WI10 NTN 3/15–3/29/11 49.7 - 930

*3-week composite sample for NC45
13

Table 1.—Concluded

NADP site Network

Represented sampling 

period

Total 

precipitation 

(mm)

Radioactive isotopes 

detected

Analyzed 

sample volume 

(mL)

NTN precipitation-depth-weighted 2-week composite samples.

WI35 NTN 3/15–3/29/11 56.2 - 807

WI36 NTN 3/14–3/29/11 24.8 - 818

WI37 NTN 3/15–3/29/11 40.1 Cs-137 978

WI98 NTN 3/15–3/29/11 57.1 - 1,000

WV04 NTN 3/15–3/29/11 35.5 - 981

WV18 NTN 3/15–3/29/11 59.2 - 842

WY02 NTN 3/15–3/29/11 11.4 - 401

Weekly MDN samples were not composited into 2-week precipitation-depth-weighted 

composite samples. MDN samples are already acidified when they are returned from the field, and they 

are treated with BrCl at the HAL. Therefore, MDN samples were analyzed by gamma spectrometry with 

no pre-processing by BQS. The MDN samples analyzed for radioactive isotope content are also

identified in table 1.

Sample Analysis by Gamma Spectrometry

Samples were analyzed by USGS at the National Reactor Facility at the Denver Federal Center, 

Denver, Colo., using gamma spectrometry with high-purity germanium (HPGe) detector systems.

Because there were only two detectors available, analysis by gamma spectrometry occurred from about 

3 to 21 weeks after the samples were collected from the NADP sites. The delay between collection and 

analysis for the first wet-deposition sample analyzed was 20 days and 5 hr for site CA99, completed at 

5:00 p.m. on April 18, 2011. The delay between collection and analysis for the last sample analyzed was 

145 days, completed on August 7, 2011 for site WA98. Two HPGe detectors were used. The first was a 

Canberra 14-percent relative efficiency detector and the second was an Ortec 40-percent relative 

efficiency detector. Detector efficiency calibrations were done for the sample-to-detector geometries 

that were used in this study. The detectors are kept at liquid-nitrogen temperature to eliminate thermal 

noise problems. Background radiation is reduced with a lead shield that surrounds the sample and 

detector.

The energy response calibration is performed with Eu-152 check sources because it emits a wide 

energy range of gamma rays, with a useable range from approximately 122 keV (thousand electron 

volts) to 1.528 MeV (million electron volts). Energy calibration checks were performed several times a 

day to ensure that the gamma peaks were within 1 keV of the measured values. Efficiency calibrations 

were done with National Institute of Standards and Technology (NIST) traceable calibration standards 

manufactured by Eckert & Ziegler, Atlanta, Ga. The efficiency calibrations were performed once and 

those calibration curves were then stored in the analyzer’s internal memory.

Two standards were used for the calibration geometry identical to the 47-mm diameter filters:

(1) 0.5 microCurie of cobalt-60 and (2) 0.055 microCurie of cesium-137 plus 0.575 microCurie of 

barium-133. These isotopes cover a gamma energy range from 88 keV to 1,332 keV. Each weekly filter 

sample obtained for the weeks ending March 22 and March 29, 2011 was analyzed in its petri dish 

container. Weekly filter samples were also composited by stacking them on the detector by site or 
14

grouping them together regionally in plastic bags. Finally, all of the filters were composited together in 

a bag, and the bag was counted for 24 hr. 

For the water samples, two standards were used: (1) 500-mL volume and (2) 1-L volume in 

standard Marinelli beakers. These standards each contained approximately one microCurie of Eu-152 

that was uniformly dispersed in the Marinelli beaker. All water samples were put into Marinelli beakers 

for the spectroscopy measurements. Two sizes of Marinelli beakers were used: (1) 500 mL and (2) 1 L.

If the sample volume was less than 500 mL and not more than 750 mL, then a 500-mL beaker was used, 

and deionized water was added if necessary to achieve a 500-mL volume. If the sample volume was 

greater than 750 mL, then 750 mL of sample was used in a 1-L Marinelli beaker without dilution. The 

750-mL volume was used instead of the full 1 L because more radioactive material is physically closer 

to the detector for the 750-mL volume than for 1 L. Data collection times were at least 6 hr per sample.

If manual observation of the gamma spectrum revealed a potential gamma peak for a fission-product or 

activation-product (for example, cobalt-60, iron-59) isotope after 6 hr, then data collection was 

continued for a longer time until sufficient data were obtained for quantification of peak areas.

The automated gamma spectrum analyzer software uses a peak search algorithm to identify 

gamma ray peaks by shape and specified ratios of isotope-specific peak area to background. The energy 

of each peak corresponds to the radioisotope that emits the associated gamma rays, and the area of the 

peak correlates to the amount of the radioisotope present in the sample. The analyzer provides the 

identified isotopes and their radioactivity levels (referred to as “activity” in this report) as a part of its 

output. The automated analyzer identified Cs-134 in one sample for CO90. Subsequently, USGS 

personnel manually reanalyzed the gamma spectra and qualitatively identified Cs-134 peaks for an 

additional 23 sites. Because these peaks were manually identified, error associated with Cs-134 

quantification cannot be evaluated. Therefore, these 23 manually derived Cs-134 values should be 

regarded as estimated. An example of a manually quantified Cs-134 peak for the sample from SD04 is 

shown in figure 4.

I-131 activities were adjusted for decay occurring between the sample-analysis stop time to the 

date and time when the collector was last open during precipitation per NADP records. The I-131 decay 

was calculated by determining the time between the collection and the analysis, calculating the number 

of half-lives that time period represented, and then dividing the analyzed I-131 activity by the value 

given by:

I-131 activity at collection time 

0.5

/

halflives

ApCi L = ; (3)

where: ApCi/L is activity of I-131 obtained at stop time of analysis, in picoCuries 

per liter (pCi/L), and

halflives is number of half-lives calculated between stop time of sample 

analysis and noon of day when last 2.5 millimeters (mm) of 

precipitation fell.

The day and time (Mountain Standard) of the last 2.5 mm of precipitation was March 26 at 3:00 

p.m. for CA66, March 27 at 12:45 a.m. at CA99, March 28 at 11:00 a.m. for CO90, March 29 at 9:30

a.m. at WA98, and March 29 at 6:45 a.m. at WA99. Cs-134 and Cs-137 activities were not adjusted for 

decay to the time of sample collection because radioactive decay during the 2-month period between 

collection and analysis was negligible for these isotopes (Wakeford, 2011).
15

Figure 4. Gamma ray spectra for wet-deposition sample from National Atmospheric Deposition Program site 

SD04 (March 22–29) with manually quantified cesium-134 peak.

Quality Assurance

The following protocols were implemented to assure the quality of the data. Four blank filter 

samples were analyzed; two filters were rinsed by filtering 250 mL of deionized water, and the other 

two were rinsed with a laboratory-prepared synthetic rainwater solution. No radioactive isotopes were 

detected in these filters.

Four blank water samples were prepared using randomly selected, cleaned, 1-L NADP Nalgene 

sample bottles and filling them with the same deionized water used to dilute the samples for gamma 

spectrometry analysis. These samples were acidified with 5 mL of the same Ultrex nitric acid used to 

acidify the real samples. No radioactive isotopes were detected in these samples.

To establish that there were no fission products in samples prior to the reported arrival of air 

masses containing emissions from the incident, archived wet-deposition samples for the week March 8–

15, 2011 for selected NTN sites were analyzed. Samples from sites CO90, IL63, NY10, VT01, and 

WA98—where Cs-137 was detected during the March 15–29, 2011 period—were analyzed by gamma 

spectrometry. No fission or activation products were detected in these samples.

Replicate samples were obtained from sites where co-located precipitation collectors are 

operated for comparison of instrumentation and estimation of variability in NTN measurements. Three 

pairs of co-located sites in operation during the study period are MA01 and 01MA at Cape Cod National 

Sea Shore, Mass.; CA50 and 50CA at Sage Hen Creek Field Station near Truckee, Calif; and CO98 and 

CO89 at Loch Vale, Rocky Mountain National Park, Colo. No fission products were detected at either 

of the co-located sites at MA01/01MA and CA50/50CA. Conversely, Cs-137 was detected for both 

CO98 (22 pCi/L) and CO89 (11 pCi/L). The CO98 and CO89 collectors are approximately 15 m apart, 

and Cs-137 activities differed by a factor of 2. The CO98 sample volume was obtained only from the 

week ending March 29, 2011 (54.9 mm precipitation depth) because the collector missed a precipitation 
16

event due to power loss during the previous week. The CO89 sample was a true 2-week composite 

representing 37.8 mm of additional precipitation during the week ending March 22, 2011. Cs-134 

activities were similar at CO98 (7.2 pCi/L) and CO89 (8.9 pCi/L).

Fission Products

None of the filter samples contained detectable fission or activation products regardless of 

compositing method, including compositing by site and region. Finally, all of the filters were grouped 

together in a bag-type geometry that was draped over the detector and counted for 24 hr, and no fission 

products were detected.

Fission products were detected in whole-water precipitation samples from 35 individual NADP 

sites (tables 1 and 2). Active NTN and MDN sites not listed in tables 1 and 2 did not collect sufficient 

sample volumes for analysis. Table 1 lists all 167 sampling sites and shows those for which no fission 

products were detected in whole-water wet-deposition samples. Table 2 provides a summary of the 

results for fission products detected in the NTN and MDN wet-deposition samples collected during 

March 15–April 5, 2011 from 35 individual NADP sites.

Spatial distributions of measured fission product isotope activities and calculated deposition 

values were mapped using a geographic information system (ESRI, 2010). The spatial distributions of I131 activities and deposition values for sites where I-131 was detected are shown in figures 5 and 6. The 

spatial distributions of measured Cs-137 and Cs-134 activities detected in wet-deposition samples and 

the calculated deposition values are shown in figures 7–10 for the 48 contiguous United States and in 

figure 11 for Alaska.
17

Table 2. Fission product isotope activities, associated precipitation depths, and calculated deposition values for National Atmospheric Deposition 

Program wet-deposition samples collected during March 15–April 5, 2011.

[NADP, National Atmospheric Deposition Program; mm, millimeters; C-134s, cesium-134; Cs-137, cesium-137; I-131, iodine-131; pCi/L, picoCuries per liter; 

Bq/m2

, Becquerels per square meter; 1 pCi = 0.037 Bq; I-131 values are adjusted for radioactive decay from time of sample analysis to noon on the last day when 

at least 2.5 mm of precipitation was measured]

NADP Site

North 

Latitude

(decimal

degrees)

West

Longitude

(decimal

degrees) Sampling Period

Total 

Precipitation 

Depth

(mm)

I-131

Activity 

(pCi/L)

Estimated

Cs-134

Activity 

(pCi/L)

Cs-137

Activity 

(pCi/L)

I-131

Deposition 

(Bq/m2)

Estimated

Cs-134

Deposition

(Bq/m2)

Cs-137

Deposition 

(Bq/m2)

AK00 53.8454 -166.5048 3/16–3/23/11 86 55 8.6 180 27

AK02 58.5139 -134.7843 3/15–3/22/11 11 7.6 3.1

AK98 57.7189 -152.5617 3/22–3/29/11 17 26 16

CA42 34.2071 -117.7618 3/22–3/29/11 170 7.3 39 46 240

CA66 36.4834 -121.1570 3/15–3/29/11 107 53.0 2.6 9.3 211 10 37

CA94 34.1938 -116.9131 3/16–3/29/11 60.2 1.1 3.0 2.6 6.7

CA99 37.7961 -119.8581 3/15–3/29/11 235 185 3.4 1,610 30

CO02 40.0547 -105.5891 3/22–3/29/11 109 11 10 43 42

CO10 38.9581 -106.9850 3/22–3/29/11 21.8 1.0 3.9 0.81 3.1

CO89 40.2878 -105.6628 3/15–3/29/11 92.7 8.9 11 31 37

CO90 40.0358 -105.5440 3/15–3/29/11 48.5 464 14 12 833 25 22

CO94 39.9939 -105.4800 3/22–3/29/11 8.6 14 4.4

CO98 40.2878 -105.6628 3/22–3/29/11 54.9 7.2 22 15 45

IL63 37.4356 -88.6719 3/22–3/29/11 20.6 6.4 15 4.9 12

IL78 40.9333 -90.7231 3/22–3/29/11 13.0 1.0 2.6 .47 1.2

MD07 39.6470 -77.4848 3/15–3/29/11 36.6 2.5 3.4

MI26 42.4103 -85.3928 3/15–3/29/11 45.2 7.0 12

MN01 45.4017 -93.2031 3/15–3/29/11 45.5 1.5 2.8 2.5 4.7

MN23 46.2494 -94.4972 3/22–3/29/11 34.3 3.0 3.8

MO03 38.7536 -92.1994 3/22–3/29/11 10.7 2.2 9.2 .89 3.6

MO05 36.9108 -90.3186 3/22–3/29/11 26.4 .80 0.80 .78 .78

MT07 46.4850 -112.0647 3/15–3/29/11 14.7 1.9 1.1

NY01 42.2280 -77.8016 3/15–3/29/11 48.5 .40 2.4 0.72 4.3

NY10 42.2994 -79.3964 3/15–3/29/11 47.0 1.8 3.1 3.1 5.4
18

Table 2.—Continued

NADP Site

North 

Latitude

(decimal

degrees)

West

Longitude

(decimal

degrees) Sampling Period

Total 

Precipitation 

Depth

(mm)

I-131

Activity 

(pCi/L)

Estimated

Cs-134

Activity 

(pCi/L)

Cs-137

Activity 

(pCi/L)

I-131

Deposition 

(Bq/m2)

Estimated

Cs-134

Deposition

(Bq/m2)

Cs-137

Deposition 

(Bq/m2)

OR10 44.2118 -122.2560 3/15–3/29/11 173 0.70 4.5

SD04 43.5577 -103.4835 3/22–3/29/11 21.6 10 20 8.0 16

SD99 44.3550 -98.2917 3/21–3/29/11 14.4 3.9 2.1

TN14 35.4688 -89.1713 3/22–3/29/11 20.0 2.0 11 1.5 8.1

VA99 37.6265 -79.5126 3/22–3/29/11 8.6 13 4.0

VT01 42.8761 -73.1633 3/15–3/22/11 18.0 0.86 3.0 0.60 2.0

WA03 48.2892 -124.6519 3/29–4/05/11 159 5.0 1.2 29 7.1

WA98 45.5639 -122.2089 3/15–3/29/11 126 1,090 1.4 5,100 6.5

WA99 46.7582 -122.1243 3/16–3/29/11 54.6 29.6 1.3 60.4 2.7

WI37 45.8228 -91.8744 3/15–3/29/11 40.1 1.9 2.9

WY99 43.8730 -104.1917 3/22–3/29/11 9.4 13 24 4.4 8.4
19

Figure 5. Spatial distribution of iodine-131 (I-131) activities in National Atmospheric Deposition Program (NADP) samples from the 48 contiguous 

United States during March 15–29, 2011.
20

Figure 6. Spatial distribution of iodine-131 (I-131) deposition calculated from measured activities and rain-gage depths from National Atmospheric 

Deposition Program (NADP) sites in the 48 contiguous United States during March 15–April 5, 2011.
21

Figure 7. Spatial distribution of estimated cesium-134 (Cs-134) activities in National Atmospheric Deposition Program (NADP) samples from the 48 

contiguous United States during March 15–29, 2011.
22

Figure 8. Spatial distribution of cesium-134 (Cs-134) deposition calculated from estimated activities and measured rain-gage depths from National 

Atmospheric Deposition Program (NADP) sites in the 48 contiguous United States during March 15–April 5, 2011.
23

Figure 9. Spatial distribution of detected cesium-137 (Cs-137) activities in National Atmospheric Deposition Program (NADP) samples from the 48 

contiguous United States during March 15–29, 2011.
24

Figure 10. Spatial distribution of cesium-137 (Cs-137) deposition calculated from measured activities and rain-gage depths from National 

Atmospheric Deposition Program (NADP) sites in the 48 contiguous United States during March 15–April 5, 2011.
25

Figure 11. Spatial distribution of cesium-134 (Cs-134) and cesium-137 (Cs-137) measured activities and 

calculated deposition values from National Atmospheric Deposition Program (NADP) sites in Alaska during 

March 15–April 5, 2011.
26

Summary and Conclusions

This study demonstrated the flexibility of the NADP in conjunction with USGS capabilities to 

monitor a sudden atmospheric release incident originating at the Fukushima Dai-Ichi Nuclear Power 

Plant near Sendai, Japan on March 12, 2011. Archived wet-only deposition samples were processed.

Filtered particulates samples were archived and analyzed by gamma spectrometry for 280 NADP 

samples. Whole-water precipitation samples (176) were analyzed by gamma spectrometry for 161 NTN 

and 6 MDN sites. Samples were collected and analyzed for the week before contaminated air arrived 

over North America (March 8–15, 2011) for five of the same sites where fission-product isotopes were 

subsequently detected during the period of March 15–April 5, 2011. No fission products were detected 

in the pre-arrival period samples. Quality-assurance data from analysis of blank samples and co-located 

site replicate measurements provide confidence in the results.

Filtered particulate samples were analyzed prior to analysis of the water samples. No fission 

products were detected on individual filters or on composited filters. Therefore, the transported fission 

products were either on particles smaller than the 0.45-μm pore size of the filter, or they were associated 

with soluble aerosol salts present in the collected samples.

I-131 was quantified and adjusted for decay to the time of sample collection for five wholewater wet-deposition samples from California, Colorado, and Washington. The activities of the 

quantified I-131 ranged from 29.6 to 1,090 pCi/L, and calculated deposition values ranged from 211 to 

5,100 Bq/m2

. Several weeks transpired between sample collection and analysis of the I-131 in the water 

samples, which were prioritized for analysis from west (high priority) to east (low priority). Therefore, 

I-131 activities likely decayed in most of the samples before they could be measured. 

Cs-134 activities were quantified for 23 samples from Alaska, California, Colorado, Illinois, 

Minnesota, Missouri, New York, South Dakota, Tennessee, Vermont, Washington, and Wyoming. The 

Cs-134 ranged from 0.40 to 55 pCi/L, and deposition values ranged from 0.47 to 180 Bq/m2

. Cs-134 

values reported for all but one site (CO90 near Nederland, Colo.) have substantial error because they 

were manually estimated from the gamma-ray spectra. Cs-137 activities were quantified for 33 samples 

from Alaska, California, Colorado, Illinois, Maryland, Michigan, Minnessota, Missouri, Montana, New 

York, Oregon, South Dakota, Tennessee, Virginia, Vermont, Washington, Wisconsin, and Wyoming. 

These samples ranged from 0.70 pCi/L to 39 pCi/L, and calculated deposition values ranged from 0.78

to 240 Bq/m2

. Cs-134 and Cs-137 activities were not adjusted for decay to date of sample collection 

because radioactive decay during the 2-month period between collection and analysis was negligible for 

these isotopes.

Acknowledgments

The following personnel are acknowledged for their valuable support of the project: Brenda 

Riney (Illinois State Water Survey) and RoseAnn Martin (USGS) who archived and processed samples 

for analysis. Brycen Roy, Alex Buehrle, and Chris Farwell (USGS) conducted gamma spectrometry 

analyses on the samples. Frontier Global Sciences is acknowledged for providing archived and 

supplemental samples for gamma spectrometry. Keith Lucey (USGS) markedly improved the quality of 

this report.
27

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